CHICAGO (AP) _ The merger of Chicago-based Unicom and Philadelphia-based PECO Energy is nearly complete, the companies said Thursday, as the Securities and Exchange Commission gave its approval for the $7.8 billion deal.

The PECO-Unicom merger will create one of the nation's largest electricity companies, with 5 million customers and annual revenues of more than $12 billion.

The companies will file with their respective states Friday to finalize the merger. Company officials say they expect to begin trading as Exelon Corp. on Monday on the New York Stock Exchange under the ticker symbol EXC. Exelon will also be listed on the Chicago and Philadelphia stock exchanges.

In March, Peco Energy agreed to cut rates by $200 million over four years, keep almost all of the jobs at its Philadelphia headquarters and maintain its charitable contributions for the next three years.

The agreement was reached with Philadelphia consumer and environmental groups, city officials and other businesses that had been questioning how the merger would benefit utility customers.

Company officials say the merger will create approximately $100 million next year in cost savings, increasing to $180 million by 2003.

``The new Exelon will create value for customers, employees and shareholders,'' said Corbin McNeill, Jr., who was named Exelon chairman and co-chief executive officer. ``Customers will gain the benefits of our combined resources and best practices, employees will have greater opportunities for career growth and shareholders will be invested in an industry leader.''

About 78 percent of Unicom shareholders supported the plan compared to 97 percent of PECO shareholders.

Unicom, parent of Commonwealth Edison, provides electrical service to about 3.5 million customers in Illinois. PECO serves about 1.5 million electric customers in the five-county Philadelphia region and more than 400,000 natural gas customers.

The new company will also control nearly 20 percent of the nation's nuclear generating capacity.